The present invention relates to a new process for preparing rubber reinforced resins, such as ASA resins, which are composites of styrene-acrylonitrile copolymers and cross-linked rubbery acrylate polymers, ABS resins which are composites of styrene-acrylonitrile copolymers and cross-linked rubbery butadiene polymers, ABSA resins which are composites of styrene-acrylonitrile copolymers with polymerized acrylate and butadiene, and high impact polystyrene resins (HIPS) which are composites of styrene homopolymers with rubbery butadiene polymers or rubbery acrylic polymers.
It is well known that styrene homopolymers and copolymers of styrene and acrylonitrile have a poor impact strength. In order to increase this impact strength, rubber is added to these styrene polymers where it acts as a reinforcing agent. One widely used method is to polymerize styrene in the presence of an unsaturated rubber. The products obtained by this method are more stable and have superior properties when compared with products prepared by other methods, such as blending or milling.
One usual technique for preparing rubber-reinforced styrenic resins is to graft chains of homopolymers or copolymers of styrene onto a rubber, either by an all emulsion process or an all suspension process or a mass-suspension process. Such techniques present an economic problem, since the manufacture of these reinforced styrenic resins depends on rubber supplies.
In order to decrease the costs of these reinforced styrenic resins and to obviate some drawbacks of the prior processes, it has been proposed to prepare rubber reinforced styrenic resins by forming the rubber particles in situ in the presence of a rigid styrenic resin. A process for this production of reinforced styrenic resins by suspension polymerization is described in U.S. patent application Ser. No. 024,837 filed on Mar. 28, 1979, U.S. Pat. No. 4,263,420, which is a continuation-in-part of application Ser. No. 916,576 filed on June 19, 1978, abandoned, which in turn is a continuation-in-part of application Ser. No. 890,211 filed on Mar. 27, 1978, abandoned, by the same applicant and assigned to the assignee hereof. The process comprises contacting a polystyrenic matrix and a monomer or a mixture of monomers capable of forming a rubbery polymer by polymerization, and then suspension polymerizing said monomer(s) to form a rubbery polymer partly grafted to the polystyrenic matrix. The production of rubber reinforced styrenic resins by this method is a batch-wise process. Moreover, the beads obtained by this suspension method must be washed, centrifuged and dried.
There exists a need in the art, therefore, for a less expensive method for producing rubber reinforced styrenic resins.